Engines may use a turbocharger to improve engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to the exhaust manifold side and the compressor is coupled to the intake manifold side. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure in the intake manifold (e.g. boost, or boost pressure) and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, such as with a wastegate.
In one example, the wastegate may include a first port coupled to boost pressure, a second port coupled to atmospheric pressure, and a valve configured to control the flow of exhaust gasses according to the wastegate duty cycle. This configuration may be referred to as a “boost-based” configuration because the force to actuate the wastegate valve comes from the boost pressure. A closed loop feedback control system may control the boost pressure by commanding the wastegate actuator to adjust the wastegate valve. However, commands to the wastegate actuator may not actually adjust the wastegate outside lower and/or upper limits of the boost pressure range. For example, at low boost pressure, the boost pressure may be too low to actuate the wastegate valve open. At high boost pressure, the wastegate valve may be actuated to an end position (e.g. wide open) and commands to open the wastegate valve further may not have the desired effect. The feedback control system may include an integral term for steady state tracking. If the feedback loop is broken (e.g. wastegate actuator commands do not have the desired effect), the integral term may introduce tracking error (e.g. integrator windup) in the feedback control system which may lead to oscillations, excessive overshoot, etc. In one solution, integrator windup may be reduced by freezing the integral term at the limits of the boost pressure. However, when the limits change due to changes in system operation, degraded control may again occur.
The inventors herein have recognized the above situation where actuation of the wastegate may be limited to a range, where the range may vary with engine operating conditions. One approach to address the above issues is a method that includes actuating the wastegate with boost pressure generated by the turbocharger. The adjustment of the wastegate actuator is limited when outside a range, where the limits of the range may vary in a specific interrelationship with boost pressure, turbine inlet pressure, turbine outlet pressure, and atmospheric pressure. In this way, the limits of the range may be used to, for example, freeze the integral term when the wastegate actuator is commanded to actuate the wastegate outside of the range. Thus, integrator windup of the feedback control system may be prevented or reduced to increase predictability of the feedback control system and to increase controllability of the boost pressure, while at the same time utilizing integrator feedback throughout as much of the range as possible.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.